Rotary Percussion and Auger Drilling

Abstract

In rotary percussion drilling, a variety of blade or roller bits (Fig. 5.2) mounted on the end of a rotating string of rods cut and break the rock. A percussion or hammer action in conjunction with a chisel bit can be used to penetrate hard material. High-pressure air pumped to the face of the bit down the centre of the rods serves to lubricate the cutting surfaces and to remove the broken rock (cuttings) by blowing it to the surface. The cuttings consist of broken, disoriented rock fragments ranging in size from silt (“rock flour”) to chips up to 3 cm diameter. In standard rotary percussion drilling, the broken rock reaches the surface along the narrow space between the drill rods and the side of the hole.